1. Field of the Invention
The present invention relates to a lens barrel and an image pickup apparatus.
2. Description of the Related Art
Image pickup apparatuses, such as a digital still camera and a video camera, are provided with a lens barrel containing a shooting optical system which leads a subject image to an image sensor.
Such a lens barrel is designed so that a focus position (a back focus position or a focusing position) of the shooting optical system for the distance of a certain subject may become a predetermined design value (in other words, the position of an image surface of the subject image formed by the shooting optical system may become the predetermined design value). However, in the lens barrel actually manufactured, there is a manufacturing error induced at the time of manufacturing a lens constituting the shooting optical system or a lens-holding mechanical component, or an assembly error induced at the time of assembling the lens and the mechanical component. Therefore, the aforementioned focus position exhibits a variation centering on the design value.
On the other hand, since the focusing of the subject image formed on an image sensor is performed by moving a focus lens (focusing group) which constitutes the shooting optical system, it is possible to absorb the variation of the focus position by the focusing group when the focus lens can move to and fro in the optical axis direction with a full amount of margin. However, when the amount of variation of the focus position is very large, or when the amount of margin before and behind the focusing group is insufficient, it is necessary to adjust the back focus position (to adjust a back focus amount) in some parts other than the focusing group in the manufacturing stage.
Adjustment methods of such a back focus amount include the method of moving an image sensor (image pickup plane) in the optical axis direction and the method of moving some lenses which constitute the shooting optical system in the optical axis direction as a back focus adjustment lens.
As a structure of moving an image sensor and a back focus adjustment lens in the optical axis direction, there is proposed a structure in which, for example, several step-wise engagement surfaces having different heights in the optical axis direction are formed in the barrel, and these engagement surfaces are selectively used to determine the position of the back focus adjustment lens in the optical axis direction (refer to JP-2002-303776 A).